The one positive with flatpak is that it allows for universal deployment. A lot of projects are providing official builds. But you are still relying on them to vet what they put in.

I haven't heard about all of these flatpak malware incidents.

I agree that Flatpak’s utilization of sandboxing is weaker in practice than is marketed. I get that many apps ship with home/host filesystem access instead of granular permissions, but it does provide meaningful isolation when used correctly.